1. Field of the Invention
The present invention relates to an improvement in a detection sensor to detect a receiving position of laser light and a level device that employs the detection sensor to detect the receiving position of laser light.
2. Description of Related Art
A detection sensor to detect a receiving position of laser light that vertically arranges a plurality of light receiving elements into an array is a conventionally known art; refer, for example, to Japanese Patent Publication Laid Open No. 2004-309440. A level device that employs the detection sensor to detect a receiving position of laser light is a similarly known art.
The detection sensor to detect a receiving position of laser light uses a respective amplifier to amplify a light receiving signal that is outputted by each respective beam receiving element, uses a respective comparator to compare the light receiving signal that is outputted by each respective amplifier with a threshold value, and deriving a central position of the laser beam in accordance with a comparison signal that is outputted by each respective comparator.
The conventional detection sensor to detect a receiving position of laser light suffers from being expensive, because it is necessary to connect each respective light receiving element with each respective amplifier and each respective comparator, which drives an increasing complexity in a circuitry configuration and results in a large number of circuit elements.
A detection sensor to detect a receiving position of laser light has thus been proposed that is capable of achieving a simplification of the circuitry configuration and reducing the number of circuit elements, i.e., WO2007/063893. Note that the detection sensor to detect a receiving position of laser light that is disclosed according to WO2007/063893 is not a conventionally known art as of the date of the present application.
The detection sensor to detect a receiving position of laser light is configured such that a plurality of light receiving elements are arranged in an array, an output element that is mutually contiguous with the light receiving element is connected via a resistor, and a light receiving position of the laser beam is derived by performing an arithmetic computation in accordance with each respective output signal that is outputted by an output line that is connected to the light receiving element that is arranged in the array, and that is present within each respective terminal of the light receiving element.
FIG. 1 is a block circuit diagram of the detection sensor to detect a receiving position of laser light that is disclosed according to WO2007/063893, wherein the detection sensor to detect a receiving position of laser light 10 comprises a light receiving element array 11X.
The light receiving element array 11X arranges an array of a light receiving element PDXi, where i is a positive integer from 1 to n+1, of a uniform shape and size, that is configured of such as a plurality of photodiodes, from either top to bottom or from left to right, i.e., in either a vertical or a horizontal direction, at, for example, an evenly spaced interval.
In the present circumstance, the evenly spaced interval means that, given a presumption that the shape of the light receiving element PDXi is a square, that a distance P between a center of a square thereof and another square thereof is mutually equal, and that an interval GL between the light receiving element PDXi and an adjacent light receiving element PDXi+1 is equivalent to a width W of the light receiving element.
The output terminals, or anodes, of each respective pair of adjacent light receiving elements are mutually connected by a resistor, i.e., a resistance value, RXj, where j is a positive integer from 1 to n. The anode of the first light receiving element PDX1 is connected to a first amplifier circuit 20X via an output line 11a, and is grounded via a resistor RXL. A cathode of each respective light receiving element PDXi is grounded by a commonly shared line 11c. 
An amplification signal that is outputted from the first amplifier circuit 20X is inputted into a first peak hold circuit 12X, an amplification signal that is outputted from a second amplifier circuit 40X is inputted into a second peak hold circuit 13X, the respective peak hold circuits 12X and 13X hold a peak value of each respective amplification signal, and each respective peak value signal is outputted to an analysis arithmetic device 60. The analysis arithmetic device 60 is configured, at a minimum, of a conversion part that converts an analog signal to a digital signal, and an arithmetic part.
A length L of the light receiving element array 11X is related, via the resistor RXj, to a voltage that is generated in a resistor RXH and the resistor RXL that are connected to the output line 11a and an output line 11b, and a laser light receiving position is derived as described hereinafter.
For purposes of convenience of description, it is presumed that a resistance value of the resistor RXL and a resistance value of the resistor RXH are equivalent to one another, and that each respective resistance value RXj is also equivalent to every other resistance value RXj. It is also presumed that the length of the light receiving array 11X is L, and further presumed that an origin O is a position midway between the first light receiving element PDX1 and the n+1 light receiving element PDXn+1.
When a spot S of a laser beam makes contact with the light receiving element PDXi of the light receiving element array 11X, an output current Ip, which is within the light receiving element PDXi, is discharged therefrom. The current Ip is split by the resistance value of the resistor RXj and discharged to the resistor RXH and the resistor RXL, whereupon a voltage VXL is generated in the output line 11b by the resistor RXL, and a voltage VXH is generated in the output line 11a by the resistor RXH.
In the present circumstance,VXH=RXH×Ip/(a sum of a resistance value ranging from a resistor RX1 to a resistor RXj−1)
Accordingly, it is possible to employ the analysis arithmetic device 60 to derive a distance Lp to the light receiving position P, using the following equation:Lp=(L/2)×(VXH−VXL)/(VXH+VXL)
Note that a level device that comprises a detection sensor to detect a receiving position of laser light of such a type as the foregoing may be employed, for example, in receiving a laser beam that is emitted by a rotary laser and measuring such as a height above a horizontal level reference plane.
As per established art, the rotary laser would, for example, emit a laser beam in a rotary manner in a horizontal direction at a given angular momentum in the direction of the rotation of the rotary axis, and the level device would, for example, be positioned in a plurality of locations in a range between, for example, five meters, i.e., close range, and 500 meters, i.e., long range, from the rotary laser, in a horizontal direction, and receive the laser beam thereupon.
Whereas a diameter of the laser beam, i.e., a spot diameter, is narrow at close range, the spot diameter increases at long range, and a time that the spot requires to traverse the light receiving element PDXi decreases at long range. Accordingly, while it is conceivable that a light receiving area of the light receiving element PDXi might be made larger in order to allow measurement thereof at long as well as short range, in general, the larger the light receiving area of the light receiving element PDXi, the lower the frequency that is responsive to the laser light, and moreover, the amplitude-frequency response with regard to the laser light also decreases as the number of the light receiving element PDXi increases. A similar effect is observed when the number of the resistor RXj increases as well.
Consequently, there is an upper bound to the number of the light receiving element PDXi and the number of the resistor RXj that are employed in a single light receiving array 11X, owing to the relation between the amplitude-frequency response with regard to the laser beam, the quantity of light in the laser beam, and the light receiving element PDXi that is employed in measuring the quantity of light in the laser beam.
Furthermore, while increasing the resistance value of the resistor RXj improves the precision of the position detector, the laser light receiving output saturates the output of the light receiving element PDXi in small stages, and thus, there is an upper bound to increasing the resistance value of the resistor RXj from the standpoint of the maximum power that is required of the laser beam.
Thus, the size and the quantity of the light receiving element PDXi, and the quantity and the resistance value of the resistor RXj, are determined in accordance with the precision and the environment that are required as the laser light receiving position, and it is consequently necessary to arrange the light receiving element array 11X in a plurality of series when the length L of a single light receiving element array 11X is insufficient for the required detection length.
In addition, while the detection sensor to detect a receiving position of laser light is configured such that a center position of the spot S of the laser beam is detected, there is no guarantee that the laser beam includes a given light amount distribution characteristic, or beam profile, i.e., a beam profile of the laser beam may not necessarily be a normal distribution, with a uniform brightness or flatness, and the detection precision degrades when the spot S of the laser beam is removed from the detection area of the light receiving element PDXi, i.e., the interval from the light receiving element PDX1 that is present at a first terminal of the light receiving element array 11X to the light receiving element PDXn+1 that is present at a second terminal thereof.
Accordingly, a configuration such as is depicted in FIG. 2 is conceivable, wherein the light receiving element array 11X and a light receiving element array 11Y are vertically arranged in a series, the origin O is treated as the position midway between the light receiving element PDXn+1 that is present at the other terminal of the upper light receiving element array 11X and the light receiving element PDX1 that is present at a first terminal of the lower light receiving element array 11Y, and the reception position of the laser beam is detected by way of a weighted average of the light receiving element arrays 11X and 11Y.
For purposes of convenience of description, in FIG. 2, a laser beam spot Smn is depicted that includes a diameter of a length that is equal to a pitch P, and a laser beam spot Smn′ is depicted that includes a diameter of a length that is equal to a 1.5 times the pitch P. The right hand side of the drawing depicts a relation between a quantity of movement of the laser beam and the output voltage, with the quantity of movement of the laser beam assigned to a horizontal axis, and the output voltage assigned to a vertical axis. It is to be understood that, in the present circumstance, output voltage corresponds to a relative ratio of the VXH and the VXL. For example, if it is presumed that a focus is on the light receiving element PDXn+1 at the other terminal of the light receiving element array 11X and the laser beam makes contact with the light receiving element PDXn+1, then the output current Ip that is outputted from the light receiving element PDXn+1 is a constant, even if the laser beam spot Smn moves by a distance Lv, and there is, accordingly, no change in the output voltage. The same is also true of the light receiving element PDX1 at a first terminal of the light receiving element array 11Y, and is also true for the balance of the light receiving elements PDXi of each respective light receiving element array 11X and 11Y.
In addition, when the laser beam spot Smn is present in the position midway between the adjacent light receiving elements PDXi, such as is depicted by a dashed line originating at the laser beam spot Smn, an output is generated that corresponds to the position midway therebetween, and the output is converted proportionally as the laser beam spot Smn moves contiguously, and a broken line-like stepped straight line BDL is obtained in an interval between the quantity of movement of the laser beam in the vertical direction and the output voltage thereof.
In addition, when the laser beam spot Smn is present between the light receiving element PDXn+1 at the other terminal of the light receiving element array 11X and the light receiving element PDX1 at a first terminal of the light receiving element array 11Y, the output of the light receiving element changes in a noncontiguous manner, and thus, the origin O may be obtained by taking a weighted average of the output of the light receiving element PDX1 of the light receiving element array 11Y and of the output of the light receiving element PDXn+1 of the light receiving element array 11X. When the diameter of the laser beam spot S is smaller than the pitch P of the light receiving element, as in the present circumstance, it is possible to derive the position of the origin O by way of the weighted average with a high degree of precision.
In the case of the laser beam spot Smn′, with the diameter of 1.5 times the pitch P, for example, when focusing on the light receiving element array 11Y, for example, as depicted in FIG. 2, the laser beam spot Smn′ changes in a straight line upon making contact with any of the light receiving elements that are associated with the light receiving element array 11Y, with an exception of the light receiving elements in a vicinity of the origin O, and, accordingly, a straight line SDL is obtained. As the laser beam spot Smn′ moves from a light receiving element PDX2 of the light receiving element array 11Y toward the origin O, however, the laser beam spot Smn′ gradually loses contact with the light receiving element PDX2 of the light receiving element array 11Y, a change occurs in an output voltage that is outputted from an output line 11a and 11b of the light receiving element array 11Y. As a consequence thereof, when the diameter of the laser beam spot Smn′ becomes greater than the pitch P, it becomes impossible to derive the position of the origin O with a high degree of precision, even when employing the weighted average.
While it would also be conceivable to overlap the light receiving element PDXn+1 that is present at the other terminal of the upper light receiving element array 11X and the light receiving element PDX1 that is present at a first terminal of the lower light receiving element array 11Y in a height direction thereof, the spot diameter of the laser beam increases, it becomes necessary to increase a quantity of the overlap thereof, and thus, the detection sensor to detect a receiving position of laser light cannot be utilized in an effective manner.